MongoDb封顶子集合 [英] MongoDb capped sub-collection

问题描述

是否可以创建一个有上限的子集合.我正在尝试做类似的事情:

Is it possible to create a capped sub-collection. I'm trying to do something like:

user = {
  name: String,
  latest_messages: [String]
}

latest_messages的上限为10.

如果没有，您有什么建议吗?

If not, what do you suggest as an alternative?

更新1:

似乎唯一手动解决的问题是保持阵列的上限.这是执行此操作的方法:

It appears as though keeping the array capped manually is the only solution. Here's a way to do this:

joe = {name: 'Joe', latest_messages: ['', '', '', '', '', '', '', '', '', '']}
db.users.save(joe)

db.users.update({name: 'Joe'}, {$push: {'latest_messages': 'hello'}})
db.users.update({name: 'Joe'}, {$pop: {'latest_messages': -1}})

db.users.update({name: 'Joe'}, {$push: {'latest_messages': 'world'}})
db.users.update({name: 'Joe'}, {$pop: {'latest_messages': -1}})

关于提高效率的任何建议吗?

Any suggestions on making this more efficient?

更新2:

有一个打开Jira票证，"SERVER-1050" ，要求添加能够将两个操作(推入和弹出)作为一个原子操作来完成.

There's an open Jira ticket, "SERVER-1050" that requests to add the ability to do the two (push & pop) as one atomic operation.

推荐答案

您只能指定上限集合的文档总数. 除非通过应用程序中的某些检查，否则无法限制数组的大小.

You can only specify the overall number of documents of a capped collection. There is no way limit the size of an array unless through some checks in your app.

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